The present invention relates to an image processing method and apparatus for changing the compression ratio of compressed image data, and a storage medium.
When a given type of phosphor is irradiated with radiation (X-rays, xcex1-rays, xcex2-rays, xcex3-rays, electron beam, ultraviolet rays, or the like), it partially stores radiation energy. When that phosphor is irradiated with excitation light such as visible light or the like, it emits light by stimulation in accordance with the stored energy. The phosphor that exhibits such nature is called a storage phosphor (photostimulable phosphor). The present applicant has already proposed a radiation image information recording/reproduction system (Japanese Patent Laid-Open Nos. 5-12429, 56-11395, and the like). In this system, using such storage phosphor, radiation image information of an object to be sensed such as a human body or the like is temporarily recorded on a storage phosphor sheet, and the storage phosphor sheet is scanned while being irradiated with excitation light such as a laser beam or the like, so as to emit light by stimulation. The emitted light is photoelectrically read to obtain an image signal, and a radiation image of the object is output as a visible image to a recording medium such as a photosensitive material or to a display device such as a CRT or the like on the basis of the image signal.
Also, a system which senses an X-ray image of an object by light emitted by stimulation using a semiconductor sensor in the same manner as in the above system has been developed in recent years. Such system has a practical merit, i.e., it can record an image over a very broader radiation exposure range than a radiation photographic system using conventional silver halide photographs. That is, X-rays over a very broad range is read by a photoelectric conversion means to be converted into an electrical signal, and a visible image based on a radiation image is output to a recording medium such as a photosensitive material or to a display device such as a CRT or the like using the electrical signal, thus obtaining a radiation image which is free from any variations of the dose of radiation.
Since such X-ray image contains a very large amount of information, storage or transmission of that image information requires a huge information volume. For this reason, storage and transmission of such image information use high-efficiency coding that reduces the data size by removing redundancy of an image or changing the contents of an image to a degree at which deterioration of image quality is not visually recognizable.
For example, JPEG recommended by ISO and ITU-T as an international standard coding scheme of still image uses DPCM for reversible compression, and discrete cosine transformation (DCT) for irreversible compression. A detailed description of JPEG will be omitted since they are described in ITU-T Recommendation T.81|ISO/IEC 10918-1 and the like.
In recent years, many studies about compression methods using discrete wavelet transformation (DWT) have been made. One feature of the compression method using DWT is that it is free from any blocking artifact which is observed in DCT.
Radiation images such as X-ray images, CT images, and MRI images prevalently used in the medical field must be held around five years by law, but hospitals hold such images over 10 years under their self-imposed control. These images are compressed at a predetermined compression ratio upon storage, but it is desirable to change the compression ratio in correspondence with the importance levels of images upon storage in terms of the storage capacity. For example, a low compression ratio is used for relatively new image data or image data which is frequently referred to, and a high compression ratio is used for old image data or image data which is rarely referred to, so as to reduce the image data size stored. However, it is not easy to change the compression ratio of image data due to huge computation volume. Also, it is required to hold image data at higher compression ratio as the image data size to be held increases.
The present invention has been made in consideration of the above prior arts, and has as its object to provide an image processing method and apparatus, which can easily obtain an image compressed at a higher compression ratio using compressed image data that has already been compressed and stored when the compression ratio of that image is changed to increase, and a storage medium.
It is another object of the present invention to provide an image processing method and apparatus which can update image files by changing the compression ratios of images in correspondence with their importance levels, and a storage medium.
It is still another object of the present invention to provide an image processing method and apparatus which can obtain image data compressed at a desired compression ratio by easily changing the compression ratio of encoded image data, and a storage medium.
It is still another object of the present invention to provide an image processing method and apparatus which can change the compression ratio of image data to a desired value by removing codes of a non-region-of-interest or a non-region-of-interest and a region of interest in units of subbands or bit planes as a feature of codes of DWT, and a storage medium.
It is still another object of the present invention to provide an image processing method and apparatus which can encode a region of interest with high image quality at a low compression ratio by preferentially removing codes of a non-region-of-interest of an image.
In order to attain the above described objects, an image processing apparatus of the present invention comprises input means for inputting compressed image data; compression ratio setting means for setting a compression ratio of the compressed image data in accordance with a time factor; and compression ratio change means for changing the compression ratio of the image data transformed by said transformation means to a compression ratio set by said compression ratio setting means.
In an aspect of the invention, the compresses image data is compressed by using a discrete wavelet transformation;
In order to attain the above described objects, an image processing apparatus of the present invention, comprises input means for inputting an image file including compressed image data; and compression ratio change means for changing a compression ratio of the image data input by said input means by deleting a code of a non-region-of-interest in the image data.
In order to attain the above described objects, an image processing apparatus of the present invention, comprises input means for inputting an image file including compressed image data; first compression ratio change means for changing a compression ratio of the image data input by said input means by deleting a code of a non-region-of-interest in the image data; and second compression ratio change means for changing the compression ratio of the image data input by said input means by deleting a code of a region of interest in the image data.
In order to attain the above described objects, an image processing method of the present invention, comprises an input step of inputting compressed image data; a compression ratio setting step of setting a compression ratio of the compressed image data in accordance with a time factor; and a compression ratio change step of changing the compression ratio of the image data transformed in said transformation step to a compression ratio set in said compression ratio setting step.
In an aspect of the present invention, the compression ratio can be set on the basis of at least one of a type of image, a sensed portion and an outpatient service history of a patient corresponding to the image data.
In another aspect of the present invention, the time factor includes at least one of the number of days elapsed after an image sensing date, the number of days elapsed after a diagnosis date based on the image, and the number of days elapsed after a last access date to the image.
In order to attain the above described objects, an image processing method of the present invention, comprises an input step of inputting an image file including compressed image data; and a compression ratio change step of changing a compression ratio of the image data input in said input step by deleting a code of a non-region-of-interest in the image data.
In order to attain the above described objects, an image processing method of the present invention, comprises an input step of inputting an image file including compressed image data; a first compression ratio change step of changing a compression ratio of the image data input in said input step by deleting a code of a non-region-of-interest in the image data; and a second compression ratio change step of changing the compression ratio of the image data input in said input step by deleting a code of a region of interest in the image data.
Other features and advantages of the present invention will be apparent form the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.